Host materials for electroluminescent devices

ABSTRACT

A composition is disclosed that includes a first compound capable of functioning as a host in an emissive layer of an OLED at room temperature; and a second compound that includes a ligand L A  of Formula III 
     
       
         
         
             
             
         
       
         
         
           
             where ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; where R represents two adjacent substituents that are joined together to form a ring that is fused to ring B, and R has a structure of Formula IV 
           
         
       
    
     
       
         
         
             
             
         
       
     
     or Formula V 
     
       
         
         
             
             
         
       
     
     disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending U.S. patent application Ser. No. 17/536,352, filed on Nov. 29, 2021, which is a continuation of U.S. patent application Ser. No. 16/272,003, filed Feb. 11, 2019, which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/641,509, filed Mar. 12, 2018. The entire contents of the above-referenced patent applications are incorporated herein by reference.

FIELD

The present invention relates to compounds for use as hosts and devices, such as organic light emitting diodes, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting diodes/devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Alternatively the OLED can be designed to emit white light. In conventional liquid crystal displays emission from a white backlight is filtered using absorption filters to produce red, green and blue emission. The same technique can also be used with OLEDs. The white OLED can be either a single EML device or a stack structure. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY

A first composition is disclosed that comprises a first compound and a second compound. The first compound has a structure according to Formula I

where ring A is fused to a structure of Formula II

where each Ar¹, Ar², and Ar³ is independently a substituted or unsubstituted six-membered aromatic ring. The second compound is capable of functioning as a phosphorescent emitter at room temperature and emits light with a peak emission wavelength equal to or greater than 550 nm. For the first composition, at least one of the following two conditions is true:

-   -   (i) the highest occupied molecular orbital of the second         compound has an energy level equal to or less than −5.1 eV; and     -   (ii) the difference in energy between the highest occupied         molecular orbital of the first compound and the highest occupied         molecular orbital of the second compound is less than 0.3 eV.

An organic light emitting device (OLED) incorporating the first composition is also disclosed. The OLED comprises a cathode, an anode, and an emissive layer disposed between the anode and cathode, where the emissive layer comprises the first composition.

A consumer product comprising the OLED incorporating the first composition is also disclosed.

A second composition is also disclosed where the second composition comprises: a first compound capable of functioning as a host in an emissive layer of an OLED device at room temperature; and a second compound comprising a ligand L_(A) of Formula III

where, ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; R represents two adjacent substituents that are joined together to form a ring that is fused to ring B, and R has a structure of Formula IV

or Formula V

where the wavy lines indicate bonds to ring B; R^(A) and R^(B) each independently represents no substitution to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; R^(A) and R^(B) are each independently a hydrogen or selected from the group consisting of the general substituents defined herein; A¹, A², A³, and A⁴ are each independently CR^(C) or N; Z¹, Z², Z³, and Z⁴ are each independently C or N; at least two adjacent of Z¹, Z², Z³, and Z⁴ are C and fuse to R; when R is Formula V, at least one of A¹, A², A³, A⁴, Z¹, Z², Z³, and Z⁴ is N; Y is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; R^(C), R¹³, R¹⁴, R′, and R″ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; any two adjacent substituents are optionally joined to form into a ring; the ligand L_(A) is coordinated to a metal M; M is Ir or Pt; the ligand L_(A) is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and M is optionally coordinated to other ligands; and at least one of the following two conditions is true:

-   -   (i) the highest occupied molecular orbital of the first compound         has an energy level equal to or less than −5.1 eV; and     -   (ii) the difference in energy between the highest occupied         molecular orbital of the first compound and the highest occupied         molecular orbital of the second compound is less than 0.3 eV.

An OLED comprising a cathode, an anode, and an emissive layer disposed between the anode and cathode is disclosed, where the emissive layer comprises the second composition described above. A consumer product comprising the OLED incorporating the second composition is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows an organic light emitting device structure used for the sample devices used to generate the experimental data disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2 .

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2 . For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and organic vapor jet printing (OVJP). Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processability than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon.

Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of electronic component modules (or units) that can be incorporated into a variety of electronic products or intermediate components. Examples of such electronic products or intermediate components include display screens, lighting devices such as discrete light source devices or lighting panels, etc. that can be utilized by the end-user product manufacturers. Such electronic component modules can optionally include the driving electronics and/or power source(s). Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. A consumer product comprising an OLED that includes the compound of the present disclosure in the organic layer in the OLED is disclosed. Such consumer products would include any kind of products that include one or more light source(s) and/or one or more of some type of visual displays. Some examples of such consumer products include flat panel displays, curved displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, rollable displays, foldable displays, stretchable displays, laser printers, telephones, mobile phones, tablets, phablets, personal digital assistants (PDAs), wearable devices, laptop computers, digital cameras, camcorders, viewfinders, micro-displays (displays that are less than 2 inches diagonal), 3-D displays, virtual reality or augmented reality displays, vehicles, video walls comprising multiple displays tiled together, theater or stadium screens, a light therapy device, and a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.), but could be used outside this temperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms “halo,” “halogen,” or “halide” as used interchangeably and refer to fluorine, chlorine, bromine, and iodine.

The term “acyl” refers to a substituted carbonyl radical (C(O)—R_(s)).

The term “ester” refers to a substituted oxycarbonyl (—O—C(O)—R_(s) or —C(O)—O—R_(s)) radical.

The term “ether” refers to an —OR_(s) radical.

The terms “sulfanyl” or “thio-ether” are used interchangeably and refer to a —SR_(s) radical.

The term “sulfinyl” refers to a —S(O)—R_(s) radical.

The term “sulfonyl” refers to a —SO₂—R_(s) radical.

The term “phosphino” refers to a —P(R_(s))₃ radical, wherein each R_(s) can be same or different.

The term “silyl” refers to a —Si(R_(s))₃ radical, wherein each R_(s) can be same or different.

In each of the above, R_(s) can be hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, and combination thereof. Preferred R_(s) is selected from the group consisting of alkyl, cycloalkyl, aryl, heteroaryl, and combination thereof.

The term “alkyl” refers to and includes both straight and branched chain alkyl radicals. Preferred alkyl groups are those containing from one to fifteen carbon atoms and includes methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, and the like. Additionally, the alkyl group may be optionally substituted.

The term “cycloalkyl” refers to and includes monocyclic, polycyclic, and spiro alkyl radicals. Preferred cycloalkyl groups are those containing 3 to 12 ring carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, bicyclo[3.1.1]heptyl, spiro[4.5]decyl, spiro[5.5]undecyl, adamantyl, and the like. Additionally, the cycloalkyl group may be optionally substituted.

The terms “heteroalkyl” or “heterocycloalkyl” refer to an alkyl or a cycloalkyl radical, respectively, having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si and Se, preferably, O, S or N. Additionally, the heteroalkyl or heterocycloalkyl group is optionally substituted.

The term “alkenyl” refers to and includes both straight and branched chain alkene radicals. Alkenyl groups are essentially alkyl groups that include at least one carbon-carbon double bond in the alkyl chain. Cycloalkenyl groups are essentially cycloalkyl groups that include at least one carbon-carbon double bond in the cycloalkyl ring. The term “heteroalkenyl” as used herein refers to an alkenyl radical having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si and Se, preferably, O, S or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl, cycloalkenyl, or heteroalkenyl group is optionally substituted.

The term “alkynyl” refers to and includes both straight and branched chain alkyne radicals. Preferred alkynyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group is optionally substituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer to an alkyl group that is substituted with an aryl group. Additionally, the aralkyl group is optionally substituted.

The term “heterocyclic group” refers to and includes aromatic and non-aromatic cyclic radicals containing at least one heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si and Se, preferably, O, S or N. Hetero-aromatic cyclic radicals may be used interchangeably with heteroaryl. Preferred hetero-non-aromatic cyclic groups are those containing 3 to 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers, such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and the like. Additionally, the heterocyclic group may be optionally substituted.

The term “aryl” refers to and includes both single-ring aromatic hydrocarbyl groups and polycyclic aromatic ring systems. The polycyclic rings may have two or more rings in which two carbons are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is an aromatic hydrocarbyl group, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. Preferred aryl groups are those containing six to thirty carbon atoms, preferably six to twenty carbon atoms, more preferably six to twelve carbon atoms. Especially preferred is an aryl group having six carbons, ten carbons or twelve carbons. Suitable aryl groups include phenyl, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl, biphenyl, triphenyl, triphenylene, fluorene, and naphthalene. Additionally, the aryl group may be optionally substituted.

The term “heteroaryl” refers to and includes both single-ring hetero-aromatic groups and polycyclic aromatic ring systems that include at least one heteroatom. The heteroatoms include, but are not limited to O, S, N, P, B, Si and Se. In many instances, O, S or N are the preferred heteroatoms. Hetero-single ring aromatic systems are preferably single rings with 5 or 6 ring atoms, and the ring can have from one to six heteroatoms. The hetero-polycyclic ring systems can have two or more rings in which two atoms are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is a heteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. The hetero-polycyclic aromatic ring systems can have from one to six heteroatoms per ring of the polycyclic aromatic ring system. Preferred heteroaryl groups are those containing three to thirty carbon atoms, preferably three to twenty carbon atoms, more preferably three to twelve carbon atoms. Suitable heteroaryl groups include dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine, preferably dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, triazine, benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogs thereof. Additionally, the heteroaryl group may be optionally substituted.

Of the aryl and heteroaryl groups listed above, the groups of triphenylene, naphthalene, anthracene, dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, pyrazine, pyrimidine, triazine, and benzimidazole, and the respective aza-analogs of each thereof are of particular interest.

The terms alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aralkyl, heterocyclic group, aryl, and heteroaryl, as used herein, are independently unsubstituted or substituted with one or more general substituents.

In many instances, the general substituents are selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some instances, the preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.

In some instances, the preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy, aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinations thereof.

In yet other instances, the more preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, aryl, heteroaryl, and combinations thereof.

The terms “substituted” and “substitution” refer to a substituent other than H that is bonded to the relevant position, e.g., a carbon or nitrogen. For example, when R¹ represents mono-substitution, then one R₁ must be other than H (i.e., a substitution). Similarly, when R¹ represents di-substitution, then two of R¹ must be other than H. Similarly, when R¹ represents no substitution, R¹, for example, can be a hydrogen for available valencies of ring atoms, as in carbon atoms for benzene and the nitrogen atom in pyrrole, or simply represents nothing for ring atoms with fully filled valencies, e.g., the nitrogen atom in pyridine. The maximum number of substitutions possible in a ring structure will depend on the total number of available valencies in the ring atoms.

As used herein, “combinations thereof” indicates that one or more members of the applicable list are combined to form a known or chemically stable arrangement that one of ordinary skill in the art can envision from the applicable list. For example, an alkyl and deuterium can be combined to form a partial or fully deuterated alkyl group; a halogen and alkyl can be combined to form a halogenated alkyl substituent; and a halogen, alkyl, and aryl can be combined to form a halogenated arylalkyl. In one instance, the term substitution includes a combination of two to four of the listed groups. In another instance, the term substitution includes a combination of two to three groups. In yet another instance, the term substitution includes a combination of two groups. Preferred combinations of substituent groups are those that contain up to fifty atoms that are not hydrogen or deuterium, or those which include up to forty atoms that are not hydrogen or deuterium, or those that include up to thirty atoms that are not hydrogen or deuterium. In many instances, a preferred combination of substituent groups will include up to twenty atoms that are not hydrogen or deuterium.

The “aza” designation in the fragments described herein, i.e. aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective aromatic ring can be replaced by a nitrogen atom, for example, and without any limitation, azatriphenylene encompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein.

As used herein, “deuterium” refers to an isotope of hydrogen. Deuterated compounds can be readily prepared using methods known in the art. For example, U.S. Pat. No. 8,557,400, Patent Pub. No. WO 2006/095951, and U.S. Pat. Application Pub. No. US 2011/0037057, which are hereby incorporated by reference in their entireties, describe the making of deuterium-substituted organometallic complexes. Further reference is made to Ming Yan, et al., Tetrahedron 2015, 71, 1425-30 and Atzrodt et al., Angew. Chem. Int. Ed. (Reviews) 2007, 46, 7744-65, which are incorporated by reference in their entireties, describe the deuteration of the methylene hydrogens in benzyl amines and efficient pathways to replace aromatic ring hydrogens with deuterium, respectively.

It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent.

Red phosphorescent emitters such as the compound RD1 shown below exhibits high efficiency, and narrow EL spectrum, which makes significant improvement to luminance efficiency (LE) of an OLED by reducing the number of long wavelength photons in the spectrum (typically above 780 nm) that are beyond the photopic response of human eye (i.e., eliminate those invisible to human eye). However, RD1 has HOMO level −5.3 eV, which makes it difficult to find a proper host compound for it. The inventive host compound H1 shown here is an example of host compounds that are suitable for red emitters having deep HOMO levels.

A first composition is disclosed that comprises a first compound and a second compound. The first compound has a structure according to Formula I

where ring A is fused to a structure of Formula II

where each Ar¹, Ar², and Ar³ is independently a substituted or unsubstituted six-membered aromatic ring. The second compound is capable of functioning as a phosphorescent emitter at room temperature and emits light with a peak emission wavelength equal to or greater than 550 nm but not greater than 1000 nm. For the first composition, at least one of the following two conditions is true:

-   -   (i) the highest occupied molecular orbital of the second         compound has an energy level equal to or less than −5.1 eV; and     -   (ii) the difference in energy between the highest occupied         molecular orbital of the first compound and the highest occupied         molecular orbital of the second compound is less than 0.3 eV.

The HOMO energy and the LUMO energy levels vs. vacuum as used herein were determined from the first oxidation and the first reduction potentials according to the following formula:

HOMO=−(CV ox)−4.8 (eV)

LUMO=−(CV red)−4.8 (eV)

The first oxidation and the first reduction potentials were measured by electrochemical method. The values were referenced to an internal ferrocene-ferroconium redox couple (Fc/Fc+) by measuring the peak potential differences from differential pulsed voltammetry. The detail procedure is described in the experimental section.

In some embodiments of the first composition, the second compound emits light with a peak emission wavelength equal to or greater than 575 nm. In some embodiments, where the second compound emits light with a peak emission wavelength equal to or greater than 600 nm.

In some embodiments of the first composition, the highest occupied molecular orbital of the second compound has an energy level equal to or less than −5.2 eV. In some embodiments, the highest occupied molecular orbital of the second compound has an energy level equal to or less than −5.3 eV.

In some embodiments of the first composition, Ar¹, Ar², and Ar³ are phenyl rings. In some embodiments, at least one of Ar¹, Ar², and Ar³ is substituted with at least one aromatic group. In some embodiments, at least one of Ar¹, Ar², and Ar³ comprises a fused carbocyclic or heterocyclic ring.

In some embodiments of the first composition, the second compound is an Ir or Pt complex having a metal-carbon bond. In some embodiments, Ir is Ir(III) and Pt is Pt(II).

In some embodiments of the first composition, the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.2 eV. In some embodiments, the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.1 eV. In some embodiments, the highest occupied molecular orbital of the first compound is lower than the highest occupied molecular orbital of the second compound.

In some embodiments of the first composition, the first compound is selected from the following group, the First Compound Group, consisting of:

In some embodiments of the first composition, the second compound has the formula of M(L¹)_(x)(L²)_(y)(L³)_(z) where, M is a metal; L¹, L², and L¹ can be the same or different;

-   -   x is 1, 2, or 3;     -   y is 0, 1, or 2;     -   z is 0, 1, or 2;     -   x+y+z is the oxidation state of the metal M;         at least one of L¹, L², and L³ has Formula III

ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; R represents two adjacent substituents that are joined together to form a ring that is fused to ring B and R has a structure of Formula IV

or Formula V

wherein the wavy lines indicate bonds to ring B; R^(A) and R^(B) each independently represents no substitution to a maximum possible number of substitutions; R^(A) and R^(B) are each independently a hydrogen or one of the general substituents defined above; A¹, A², A³, and A⁴ are each independently CR^(c) or N; Z¹, Z², Z³, and Z⁴ are each independently C or N; at least two adjacent of Z¹, Z², Z³, and Z⁴ are C and fuse to R; when R is Formula V, at least one of A¹, A², A³, A⁴, Z¹, Z², Z³, and Z⁴ is N; Y is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; R^(C), R¹³, R¹⁴, R′, and R″ are each independently a hydrogen or one of the general substituents defined above; and any two adjacent substituents are optionally joined to form into a ring.

In some embodiments of the first composition, in which the second compound has the formula of M(L′)_(x)(L²)_(y)(L³)_(z), as defined above, R^(A) and R^(B) are each independently a hydrogen or one of the preferred general substituents or the group consisting of the more preferred general substituents defined above; and R^(C), R¹³, R¹⁴, R′, and R″ are each independently a hydrogen or one of the preferred general substituents defined above.

In some embodiments of the first composition, in which the second compound has the formula of M(L′)_(x)(L²)_(y)(L³)_(z), as defined above, the second compound has a formula of M(L′)₂L², where L¹ has a formula according to Formula III, and L² is an unsubstituted or substituted acetylacetonate ligand.

In some embodiments of the first composition, the second compound is a transition metal complex comprising at least one ligand or part of the ligand, if the ligand is more than bidentate, selected from the following group, the Ligand Group, consisting of:

-   -   where R¹ and R² represent mono to a maximum possible number of         substitutions, or no substitution; wherein each R¹ and R² is         independently a hydrogen or one of the general substituents         defined above; and where any two substituents may be joined or         fused together to form a ring.

In some embodiments of the first composition, the second compound is selected from the following group, the Second Compound Group, consisting of:

In some embodiments of the first composition, where the first compound is a host, and where the composition comprises a third compound, which serves as a co-host. In some embodiments, where the third compound has a highest occupied molecular orbital that is equal to or greater than −5.3 eV.

In some embodiments of the first composition, the composition comprises a third compound, wherein the third compound has a highest occupied molecular orbital that is equal to or greater than −5.2 eV.

In some embodiments, the first composition further comprises a third compound, wherein the third compound has a highest occupied molecular orbital that is equal to or greater than −5.1 eV. In some embodiments, the third compound is selected from the group consisting of the following compounds:

In some embodiments of the composition, in which the second compound has the formula of M(L¹)_(x)(L²)_(y)(L³)_(z),

wherein R³ to R¹² each independently represents no substitution to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein each of R³ to R¹² is independently a hydrogen or one of the general substituents defined above; wherein Ar⁴-Ar⁸ are each independently a 6-membered carbocyclic or heterocyclic ring; wherein m=0, 1, 2, or 3; and wherein any two substituents may be joined or fused together to form a ring.

In some embodiments of the first composition, the third compound is selected from the group consisting of:

An organic light emitting device (OLED) incorporating the first composition is also disclosed. The OLED comprises a cathode, an anode, and an emissive layer disposed between the anode and cathode. The emissive layer comprises the first composition described above.

A consumer product comprising the OLED incorporating the first composition is also disclosed. Examples of consumer product types are described above.

A second composition is also disclosed where the second composition comprises: a first compound capable of functioning as a host in an emissive layer of an OLED device at room temperature; and a second compound comprising a ligand L_(A) of Formula III

where, ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; R represents two adjacent substituents that are joined together to form a ring that is fused to ring B, and R has a structure of Formula IV

or Formula V

where the wavy lines indicate bonds to ring B; R^(A) and R^(B) each independently represents no substitution to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; R^(A) and R^(B) are each independently a hydrogen or selected from the group consisting of the general substituents defined above; A¹, A², A³, and A⁴ are each independently CR^(C) or N; Z¹, Z², Z³, and Z⁴ are each independently C or N; at least two adjacent of Z¹, Z², Z³, and Z⁴ are C and fuse to R; when R is Formula V, at least one of A¹, A², A³, A⁴, Z¹, Z², Z³, and Z⁴ is N; Y is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; R^(C), R¹³, R¹⁴, R′, and R″ are each independently a hydrogen or selected from the group consisting of general substituents defined above; any two adjacent substituents are optionally joined to form into a ring; the ligand L_(A) is coordinated to a metal M; M is Ir or Pt; the ligand L_(A) is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and M is optionally coordinated to other ligands; and at least one of the following two conditions is true:

-   -   (i) the highest occupied molecular orbital of the first compound         has an energy level equal to or less than −5.1 eV; and     -   (ii) the difference in energy between the highest occupied         molecular orbital of the first compound and the highest occupied         molecular orbital of the second compound is less than 0.3 eV.

In some embodiments of the second composition, M is Ir(III) or Pt(II).

In some embodiments of the second composition, at least one of R¹³ and R¹⁴ comprises a chemical group selected from the group consisting of alkyl, cycloalkyl, partially fluorinated alkyl, partially fluorinated cycloalkyl, and combinations thereof.

In some embodiments of the second composition, R^(A) and R^(B) are each independently a hydrogen or one of the preferred general substituents defined above; and where R^(C), R¹³, R¹⁴, R′, and R″ are each independently a hydrogen or one of the preferred general substituents defined above.

In some embodiments of the second composition, the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.2 eV. In some embodiments, the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.1 eV. In some embodiments, the highest occupied molecular orbital of the first compound is lower than the highest occupied molecular orbital of the second compound.

In some embodiments of the second composition, the highest occupied molecular orbital of the first compound has an energy equal to or less than −5.2 eV. In some embodiments, where the highest occupied molecular orbital of the first compound has an energy equal to or less than −5.3 eV.

In some embodiments of the second composition, the first compound is selected from the group consisting of the compounds from the First Compound Group.

In some embodiments of the second composition, the second compound comprises a ligand selected from the Ligand Group.

In some embodiments of the second composition, the second compound is selected from the group consisting of the compounds from the Second Compound Group.

According to some embodiments, an OLED comprising a cathode, an anode, and an emissive layer disposed between the anode and cathode is disclosed, where the emissive layer comprises the second composition described above. A consumer product comprising, or incorporated therein, the OLED is also disclosed.

A formulation comprising the composition or the second composition of the present disclosure is also disclosed.

In some embodiments, the OLED has one or more characteristics selected from the group consisting of being flexible, being rollable, being foldable, being stretchable, and being curved. In some embodiments, the OLED is transparent or semi-transparent. In some embodiments, the OLED further comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising a delayed fluorescent emitter. In some embodiments, the OLED comprises a RGB pixel arrangement or white plus color filter pixel arrangement. In some embodiments, the OLED is a mobile device, a hand held device, or a wearable device. In some embodiments, the OLED is a display panel having less than 10 inch diagonal or 50 square inch area. In some embodiments, the OLED is a display panel having at least 10 inch diagonal or 50 square inch area. In some embodiments, the OLED is a lighting panel.

An emissive region in an OLED is also disclosed. The emissive region comprises a first composition that comprises a first compound and a second compound. The first compound has a structure according to Formula I

where ring A is fused to a structure of Formula II

where each Ar¹, Ar², and Ar³ is independently a substituted or unsubstituted six-membered aromatic ring. The second compound is capable of functioning as a phosphorescent emitter at room temperature and emits light with a peak emission wavelength equal to or greater than 550 nm but not greater than 1000 nm. For the first composition, at least one of the following two conditions is true:

-   -   (i) the highest occupied molecular orbital of the second         compound has an energy level equal to or less than −5.1 eV; and     -   (ii) the difference in energy between the highest occupied         molecular orbital of the first compound and the highest occupied         molecular orbital of the second compound is less than 0.3 eV.

According to another aspect, a formulation comprising the compound described herein is also disclosed.

The OLED disclosed herein can be incorporated into one or more of a consumer product, an electronic component module, and a lighting panel.

In yet another aspect of the present disclosure, a formulation that comprises the novel compound disclosed herein is described. The formulation can include one or more components selected from the group consisting of a solvent, a host, a hole injection material, hole transport material, electron blocking material, hole blocking material, and an electron transport layer material, disclosed herein.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants to substantially alter its density of charge carriers, which will in turn alter its conductivity. The conductivity is increased by generating charge carriers in the matrix material, and depending on the type of dopant, a change in the Fermi level of the semiconductor may also be achieved. Hole-transporting layer can be doped by p-type conductivity dopants and n-type conductivity dopants are used in the electron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: EP01617493, EP01968131, EP2020694, EP2684932, US20050139810, US20070160905, US20090167167, US2010288362, WO06081780, WO2009003455, WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804, US20150123047, and US2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but are not limited to: a phthalocyanine or porphyrin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and silane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but are not limited to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and the group consisting of 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Each Ar may be unsubstituted or may be substituted by a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH) or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are not limited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40; (Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independently selected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In another aspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met is selected from Ir, Pt, Os, and Zn. In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc*/Fc couple less than about 0.6 V.

Non-limiting examples of the HIL and HTL materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: CN102702075, DE102012005215, EP01624500, EP01698613, EP01806334, EP01930964, EP01972613, EP01997799, EP02011790, EP02055700, EP02055701, EP1725079, EP2085382, EP2660300, EP650955, JP07-073529, JP2005112765, JP2007091719, JP2008021687, JP2014-009196, KR20110088898, KR20130077473, TW201139402, U.S. Ser. No. 06/517,957, US20020158242, US20030162053, US20050123751, US20060182993, US20060240279, US20070145888, US20070181874, US20070278938, US20080014464, US20080091025, US20080106190, US20080124572, US20080145707, US20080220265, US20080233434, US20080303417, US2008107919, US20090115320, US20090167161, US2009066235, US2011007385, US20110163302, US2011240968, US2011278551, US2012205642, US2013241401, US20140117329, US2014183517, U.S. Pat. Nos. 5,061,569, 5,639,914, WO05075451, WO07125714, WO08023550, WO08023759, WO2009145016, WO2010061824, WO2011075644, WO2012177006, WO2013018530, WO2013039073, WO2013087142, WO2013118812, WO2013120577, WO2013157367, WO2013175747, WO2014002873, WO2014015935, WO2014015937, WO2014030872, WO2014030921, WO2014034791, WO2014104514, WO2014157018,

EBL:

An electron blocking layer (EBL) may be used to reduce the number of electrons and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies, and/or longer lifetime, as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and/or higher triplet energy than the emitter closest to the EBL interface. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and/or higher triplet energy than one or more of the hosts closest to the EBL interface. In one aspect, the compound used in EBL contains the same molecule or the same functional groups used as one of the hosts described below.

Additional Hosts:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting dopant material, and may contain one or more additional host materials using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. Any host material may be used with any dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have the following general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴ are independently selected from C, N, O, P, and S; L¹⁰¹ is an another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, Met is selected from Ir and Pt. In a further aspect, (Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

In one aspect, the host compound contains at least one of the following groups selected from the group consisting of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, host compound contains at least one of the following groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen, deuteriumn, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above. k is an integer from 0 to 20 or 1 to 20. X¹⁰¹ to X¹⁰⁸ are independently selected from C (including CH) or N. Z¹⁰¹ and Z¹⁰² are independently selected from NR¹⁰¹, O, or S.

Non-limiting examples of the additional host materials that may be used in an OLED in combination with the host compound disclosed herein are exemplified below together with references that disclose those materials: EP2034538, EP2034538A, EP2757608, JP2007254297, KR20100079458, KR20120088644, KR20120129733, KR20130115564, TW201329200, US20030175553, US20050238919, US20060280965, US20090017330, US20090030202, US20090167162, US20090302743, US20090309488, US20100012931, US20100084966, US20100187984, US2010187984, US2012075273, US2012126221, US2013009543, US2013105787, US2013175519, US2014001446, US20140183503, US20140225088, US2014034914, U.S. Pat. No. 7,154,114, WO2001039234, WO2004093207, WO2005014551, WO2005089025, WO2006072002, WO2006114966, WO2007063754, WO2008056746, WO2009003898, WO2009021126, WO2009063833, WO2009066778, WO2009066779, WO2009086028, WO2010056066, WO2010107244, WO2011081423, WO2011081431, WO2011086863, WO2012128298, WO2012133644, WO2012133649, WO2013024872, WO2013035275, WO2013081315, WO2013191404, WO2014142472, US20170263869, US20160163995, U.S. Pat. No. 9,466,803.

Emitter:

An emitter example is not particularly limited, and any compound may be used as long as the compound is typically used as an emitter material. Examples of suitable emitter materials include, but are not limited to, compounds which can produce emissions via phosphorescence, fluorescence, thermally activated delayed fluorescence, i.e., TADF (also referred to as F-type delayed fluorescence; see, e.g., U.S. application Ser. No. 15/700,352, which is hereby incorporated by reference in its entirety), triplet-triplet annihilation, or combinations of these processes. In some embodiments, the emissive dopant can be a racemic mixture, or can be enriched in one enantiomer.

Non-limiting examples of the emitter materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526, EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B3, EP2062907, EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652, KR20120032054, KR20130043460, TW201332980, U.S. Ser. No. 06/699,599, U.S. Ser. No. 06/916,554, US20010019782, US20020034656, US20030068526, US20030072964, US20030138657, US20050123788, US20050244673, US2005123791, US2005260449, US20060008670, US20060065890, US20060127696, US20060134459, US20060134462, US20060202194, US20060251923, US20070034863, US20070087321, US20070103060, US20070111026, US20070190359, US20070231600, US2007034863, US2007104979, US2007104980, US2007138437, US2007224450, US2007278936, US20080020237, US20080233410, US20080261076, US20080297033, US200805851, US2008161567, US2008210930, US20090039776, US20090108737, US20090115322, US20090179555, US2009085476, US2009104472, US20100090591, US20100148663, US20100244004, US20100295032, US2010102716, US2010105902, US2010244004, US2010270916, US20110057559, US20110108822, US20110204333, US2011215710, US2011227049, US2011285275, US2012292601, US20130146848, US2013033172, US2013165653, US2013181190, US2013334521, US20140246656, US2014103305, U.S. Pat. Nos. 6,303,238, 6,413,656, 6,653,654, 6,670,645, 6,687,266, 6,835,469, 6,921,915, 7,279,704, 7,332,232, 7,378,162, 7,534,505, 7,675,228, 7,728,137, 7,740,957, 7,759,489, 7,951,947, 8,067,099, 8,592,586, 8,871,361, WO06081973, WO06121811, WO07018067, WO07108362, WO07115970, WO07115981, WO08035571, WO2002015645, WO2003040257, WO2005019373, WO2006056418, WO2008054584, WO2008078800, WO2008096609, WO2008101842, WO2009000673, WO2009050281, WO2009100991, WO2010028151, WO2010054731, WO2010086089, WO2010118029, WO2011044988, WO2011051404, WO2011107491, WO2012020327, WO2012163471, WO2013094620, WO2013107487, WO2013174471, WO2014007565, WO2014008982, WO2014023377, WO2014024131, WO2014031977, WO2014038456, WO2014112450,

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies and/or longer lifetime as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. In some embodiments, the HBL material has a lower HOMO (further from the vacuum level) and or higher triplet energy than the emitter closest to the HBL interface. In some embodiments, the HBL material has a lower HOMO (further from the vacuum level) and or higher triplet energy than one or more of the hosts closest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or the same functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ is an integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above. Ar¹ to Ar³ has the similar definition as Ar's mentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL include, but are not limited to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

Non-limiting examples of the ETL materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: CN103508940, EP01602648, EP01734038, EP01956007, JP2004-022334, JP2005149918, JP2005-268199, KR0117693, KR20130108183, US20040036077, US20070104977, US2007018155, US20090101870, US20090115316, US20090140637, US20090179554, US2009218940, US2010108990, US2011156017, US2011210320, US2012193612, US2012214993, US2014014925, US2014014927, US20140284580, U.S. Pat. Nos. 6,656,612, 8,415,031, WO2003060956, WO2007111263, WO2009148269, WO2010067894, WO2010072300, WO2011074770, WO2011105373, WO2013079217, WO2013145667, WO2013180376, WO2014104499, WO2014104535,

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in the performance, which is composed of an n-doped layer and a p-doped layer for injection of electrons and holes, respectively. Electrons and holes are supplied from the CGL and electrodes. The consumed electrons and holes in the CGL are refilled by the electrons and holes injected from the cathode and anode, respectively; then, the bipolar currents reach a steady state gradually. Typical CGL materials include n and p conductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated. Thus, any specifically listed substituent, such as, without limitation, methyl, phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated, and fully deuterated versions thereof. Similarly, classes of substituents such as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. also encompass undeuterated, partially deuterated, and fully deuterated versions thereof.

Experimental

In order to understand the compatibility of specific hosts with RD1 type emitters having deep HOMO levels, HOMO, LUMO, and triplet energy levels (T1) have been measured for emissive layer materials. Solution cyclic voltammetry and differential pulsed voltammetry were performed using a CH Instruments model 6201B potentiostat using anhydrous dimethylformamide solvent and tetrabutylammonium hexafluorophosphate as the supporting electrolyte. Glassy carbon, and platinum and silver wires were used as the working, counter and reference electrodes, respectively. Electrochemical potentials were referenced to an internal ferrocene-ferroconium redox couple (Fc/Fc+) by measuring the peak potential differences from differential pulsed voltammetry. The corresponding HOMO energy and the LUMO energy levels vs. vacuum as used herein were determined from the first oxidation and the first reduction potentials according to the following formula:

HOMO=−(CV ox)−4.8 (eV)

LUMO=−(CV red)−4.8 (eV)

T1: Less than 1 mg of material was dissolved by ultrasonication in 2 mL of 2-methyltetrahydrofuran solvent. The solution was filtered through a 2 micron filter into a quartz tube. The tube was sealed with a rubber septum and bubble degassed with nitrogen in order to prevent oxygen quenching. The phosphorescence spectrum was carried out on a Horiba Jobin Yvon Fluorolog-3 system equipped with a Xenon lamp at low temperature close to 77° K. The T1 level was determined using photoluminescence (PL) at 77° K. T1 (eV) is defined as 1240/triplet wavelength. The HOMO, LUMO energy levels, and T1 level are summarized in Table 1 below.

TABLE 1 HOMO, LUMO and T1 energy levels of emissive layer materials in the device examples. Compound HOMO [eV] LUMO [eV] T1 [eV] RD1 −5.32 −2.81 2.02 H1 −5.36 −2.78 2.55 CH1 −5.67 −2.92 2.37 CH2 −5.43 −2.88 2.40 CH3 −5.64 −2.73 2.73 HH1 −5.11 −2.37 2.31

Sample OLEDs were fabricated to compare the beneficial effects of the novel hosts of the present disclosure used as hosts for deep HOMO red emitters against comparative hosts in both single and dual host structures. All sample devices were fabricated by high vacuum (<10⁻⁷ Torr) thermal evaporation. The anode electrode was 1,150 Å of indium tin oxide (ITO). All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂) immediately after fabrication, and a moisture getter was incorporated inside the device package. Referring to FIG. 3 , the organic stack 300 of the device examples consisted of sequentially, from the ITO anode surface 310, 100 Å of HAT-CN as the hole injection layer (HIL) 315; 450 Å of HTM as a hole transporting layer (HTL) 320; 400 Å of an emissive layer (EML) 325 containing a host compound, hole-transporting cohost (if any), and 3% of red emitter compound RD1 having a deep HOMO level, and 350 Å of Liq (8-hydroxyquinoline lithium) doped with 35% of ETM as the electron transporting layer (ETL) 330. The OLED structure was topped off with 10 Å of Liq (8-hydroxyquinoline lithium) as electron injection layer (EIL) 335 and 1,000 Å of Al as cathode 340. The host and hole transporting cohosts were selected to provide the improvement in the device's operating voltage and efficiency. The hole transporting cohost was added to the electron-transporting host H1 or CH3 in some cases to help transporting positive charge in the emissive layer. The devices, Example 1 and Example 2, were fabricated with the novel host/emitter composition comprising the host compound H1 and the red emitter RD1. The comparative example devices, CE1, CE2, and CE3 were fabricated with comparative host compounds CH1, CH2, and CH3, respectively, in the EML. Table 2 below summarizes the thickness and the materials used for the layers in the sample devices.

TABLE 2 Device layer materials and thicknesses Layer Material Thickness [Å] Anode ITO 1,150 HIL HAT-CN 100 HTL HTM 450 EML Host: H-transporting 400 cohost (if any): RD1 3% ETL Liq: ETM 35% 350 EIL Liq 10 Cathode A1 1,000

The chemical structures of the materials used are shown below.

The device performance normalized data are summarized in Table 3 below.

TABLE 3 At 10 mA/cm² Voltage LE EQE Device H- λmax (normal- (normal- (normal- Example Host cohost [nm] ized) ized) ized) Example 1 H1 629 84% 106% 105% CE1 CH1 629 100%  100% 100% CE2 CH2 628 92% 106%  95% Example 2 H1 HH1 630 95% 110% 109% CE3 CH3 HH1 628 100%  100% 100%

In the above table, Example 1 is compared with CE1 and CE2, and normalized to CE1. Example 2 is compared with CE3, and normalized to CE3. The inventive host compound H1, when used in a single host device Example 1, exhibited the lowest voltage and the highest EQE at 10 mA/cm² vs. comparative devices CE1 (84% V and 105% EQE vs. CE1) and CE2 (91% V and 110% EQE vs. CE2) containing the host compounds CH1 and CH2, respectively. Therefore, the combination of the host H1 with emitter RD1 provides the unexpected lowest voltage, and highest efficiency in the device performance.

The inventive host compound H1, when used in a dual host device Example 2, exhibited operating voltage that is lower (95%) and an EQE that is higher (109%) vs. comparative device CE3 containing the host compound CH3. The second host material was compound HH1 in both inventive and comparative examples. This also reveals the advantage of the inventive formulation by combining host compounds claimed here, such as H1, and the deep HOMO type emitters, such as RD1.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

We claim:
 1. A composition comprising: a first compound capable of functioning as a host in an emissive layer of an organic light emitting device at room temperature; and a second compound comprising a ligand L_(A) of Formula III

 wherein ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; wherein R represents two adjacent substituents that are joined together to form a ring that is fused to ring B, and R has a structure of Formula IV

or Formula V

wherein the wavy lines indicate bonds to ring B; wherein R^(A) represents two substitutions to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein R^(B) represents no substitution to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein R^(A) and R^(B) are each independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein two adjacent R^(A) are joined to form a ring; wherein A¹, A², A³, and A⁴ are each independently CR^(C) or N; wherein Z¹, Z², Z³, and Z⁴ are each independently C or N; wherein at least two adjacent of Z¹, Z², Z³, and Z⁴ are C and fuse to R; wherein when R is Formula V, at least one of A¹, A², A³, A⁴, Z¹, Z², Z³, and Z⁴ is N; wherein Y is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; wherein R^(C), R¹³, R¹⁴, R′, and R″ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein any two adjacent substituents are optionally joined to form into a ring; wherein the ligand L_(A) is coordinated to a metal M; wherein M is Ir or Pt; wherein the ligand L_(A) is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and wherein M is optionally coordinated to other ligands; and wherein at least one of the following two conditions is true: (i) the highest occupied molecular orbital of the first compound has an energy level equal to or less than −5.1 eV; and (ii) the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.3 eV.
 2. The composition of claim 1, wherein at least one of R¹³ and R¹⁴ comprises a chemical group selected from the group consisting of alkyl, cycloalkyl, partially fluorinated alkyl, partially fluorinated cycloalkyl, and combinations thereof.
 3. The composition of claim 1, wherein R¹³ and R¹⁴ are joined to form a ring.
 4. The composition of claim 1, wherein R¹³ and R¹⁴ are not hydrogen.
 5. The composition of claim 1, wherein one of R¹³ and R¹⁴ comprises a ring structure and the other of R¹³ and R¹⁴ comprises alkyl.
 6. The composition of claim 5, wherein the ring structure can be cycloalkyl, heterocycloalkyl, cycloalkenyl, aryl, heteroaryl, and combinations thereof.
 7. The compound of claim 1, wherein two adjacent R_(C) are joined to form a ring.
 8. The composition of claim 1, wherein R^(A) is a substituent selected from the group consisting of fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof; wherein R^(B) is a hydrogen or a substituent selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof; and R^(C), R¹³, R¹⁴, R′, and R″ are each independently selected from the group consisting of hydrogen, deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.
 9. The composition of claim 1, wherein the second compound has a formula of M(L_(A))₂L², wherein L² is an unsubstituted or substituted acetylacetonate ligand.
 10. The composition of claim 1, wherein the second compound emits light with a peak emission wavelength equal to or greater than 600 nm, wherein at least one of the following two conditions is true: (iii) the highest occupied molecular orbital of the second compound has an energy level equal to or less than −5.3 eV; and (iv) the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.1 eV.
 11. The composition of claim 1, wherein the second compound is a transition metal complex comprising at least one ligand selected from the group consisting of:

wherein R¹ and R² represent mono to a maximum possible number of substitutions, or no substitution; wherein each R¹ and R² is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two substituents may be joined or fused together to form a ring.
 12. The composition of claim 1, wherein the second compound is selected from the group consisting of:


13. The composition of claim 1, wherein the first compound is a compound of Formula I

wherein ring A is fused to a structure of Formula II:

wherein each Ar¹, Ar², and Ar³ is independently a substituted or unsubstituted six-membered aromatic ring; and the second compound is capable of functioning as a phosphorescent emitter at room temperature; wherein the second compound emits light with a peak emission wavelength equal to or greater than 550 n; wherein at least one of the following two conditions is true: (i) the highest occupied molecular orbital of the second compound has an energy level equal to or less than −5.1 eV; and (ii) the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.3 eV.
 14. The composition of claim 11, wherein Ar¹, Ar², and Ar³ are phenyl rings.
 15. The composition of claim 11, wherein at least one of Ar¹, Ar², and Ar³ comprises a fused carbocyclic or heterocyclic ring.
 16. The composition of claim 1, wherein the composition comprises a third compound, which serves as a co-host.
 17. An organic light emitting device (OLED) comprising: a cathode; an anode; and an emissive layer, disposed between the anode and cathode; wherein the emissive layer comprises a composition comprising: a first compound capable of functioning as a host in an emissive layer of the OLED at room temperature; and a second compound comprising a ligand L_(A) of Formula III

 wherein ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; wherein R represents two adjacent substituents that are joined together to form a ring that is fused to ring B, and R has a structure of Formula IV

or Formula V

wherein the wavy lines indicate bonds to ring B; wherein R^(A) represents two substitutions to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein R^(B) represents no substitution to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein R^(A) and R^(B) are each independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein two adjacent R^(A) are joined to form a ring; wherein A¹, A², A³, and A⁴ are each independently CR^(c) or N; wherein Z¹, Z², Z³, and Z⁴ are each independently C or N; wherein at least two adjacent of Z¹, Z², Z³, and Z⁴ are C and fuse to R; wherein when R is Formula V, at least one of A¹, A², A³, A⁴, Z¹, Z², Z³, and Z⁴ is N; wherein Y is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; wherein R^(C), R¹³, R¹⁴, R′, and R″ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein any two adjacent substituents are optionally joined to form into a ring; wherein the ligand L_(A) is coordinated to a metal M; wherein M is Ir or Pt; wherein the ligand L_(A) is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and wherein M is optionally coordinated to other ligands; and wherein at least one of the following two conditions is true: (i) the highest occupied molecular orbital of the first compound has an energy level equal to or less than −5.1 eV; and (ii) the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.3 eV.
 18. The OLED of claim 17, wherein at least one of R¹³ and R¹⁴ comprises a chemical group selected from the group consisting of alkyl, cycloalkyl, partially fluorinated alkyl, partially fluorinated cycloalkyl, and combinations thereof.
 19. A consumer product comprising an organic light-emitting device (OLED) comprising: an anode; a cathode; and an emissive layer, disposed between the anode and cathode; wherein the emissive layer comprises a composition comprising: a first compound capable of functioning as a host in an emissive layer of the OLED at room temperature; and a second compound comprising a ligand L_(A) of Formula III

 wherein ring A is a 5-membered or 6-membered carbocyclic or heterocyclic ring; wherein R represents two adjacent substituents that are joined together to form a ring that is fused to ring B, and R has a structure of Formula IV

or Formula V

wherein the wavy lines indicate bonds to ring B; wherein R^(A) represents two substitutions to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein R^(B) represents no substitution to a maximum possible number of substitutions on a ring carbon the substituents are attached thereto; wherein R^(A) and R^(B) are each independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein two adjacent R^(A) are joined to form a ring; wherein A¹, A², A³, and A⁴ are each independently CR^(c) or N; wherein Z¹, Z², Z³, and Z⁴ are each independently C or N; wherein at least two adjacent of Z¹, Z², Z³, and Z⁴ are C and fuse to R; wherein when R is Formula V, at least one of A¹, A², A³, A⁴, Z¹, Z², Z³, and Z⁴ is N; wherein Y is selected from the group consisting of BR′, NR′, PR′, O, S, Se, C═O, S═O, SO₂, CR′R″, SiR′R″, and GeR′R″; wherein R^(C), R¹³, R¹⁴, R′, and R″ are each independently selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein any two adjacent substituents are optionally joined to form into a ring; wherein the ligand L_(A) is coordinated to a metal M; wherein M is Ir or Pt; wherein the ligand L_(A) is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate, or hexadentate ligand; and wherein M is optionally coordinated to other ligands; and wherein at least one of the following two conditions is true: (i) the highest occupied molecular orbital of the first compound has an energy level equal to or less than −5.1 eV; and (ii) the difference in energy between the highest occupied molecular orbital of the first compound and the highest occupied molecular orbital of the second compound is less than 0.3 eV.
 20. The consumer product of claim 19, wherein at least one of R¹³ and R¹⁴ comprises a chemical group selected from the group consisting of alkyl, cycloalkyl, partially fluorinated alkyl, partially fluorinated cycloalkyl, and combinations thereof. 